Method for manufacturing sensor element for use in gas sensor, inspecting electrical characteristics of sensor element, and pre-treating sensor element
a technology for gas sensors and sensor elements, applied in chemical methods analysis, instruments, material analysis, etc., can solve the problems of gas sensor loss of measurement accuracy set in its specification, reduction in production yield, and unstable condition of sensor elements obtained after aging processes, so as to achieve high reliability, ensure sensitivity characteristics, and improve production yield
Active Publication Date: 2013-10-03
NGK INSULATORS LTD
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Benefits of technology
The patent describes a method for treating a sensor element to improve its inspection process. The method involves applying a voltage to the sensor element to remove any gas components attached to its surface before inspecting its electrical characteristics. This helps to stabilize the condition of the electrodes, preventing incorrect decisions during the inspection process and ensuring reliable sensitivity characteristics. Ultimately, this method improves the production yield and reliability of the gas sensor.
Problems solved by technology
However, actually, oxygen originally existing in the measurement gas is, though removed prior to the decomposition of the object gas component, left in a small amount and is decomposed, so that a current slightly flows.
If the actual sensitivity characteristics change over time, the concentration value which is calculated based on the sensitivity characteristics determined at the time of shipment loses its reliability as the use of the gas sensor continues, and eventually the gas sensor loses a measurement accuracy set in its specification.
However, the condition of an electrode of a sensor element obtained after an aging process is not stabilized because, for example, the degree of oxidation during baking of the element and the degree of reduction during the aging in a rich atmosphere, which is performed after the baking, are not constant, and a rich component that is left within the sensor element after the aging is suddenly decomposed.
Inspecting the element characteristics and further determining the sensitivity characteristics under such an unstabilized state may cause an erroneous determination in which a sensor element that is actually a non-defective product is determined as a defective product.
This results in a reduction in the production yield.
The pre-treatment method disclosed in Japanese Patent Application Laid-Open No. 2011-145285 exerts an effect of stabilizing the electrode of the sensor element, but the effect is not always constant.
Thus, there is a problem that an improvement in the production yield is limited.
Additionally, there is also a problem that this method cannot always be regarded as a satisfactory method from the viewpoint of the productivity of the sensor element, because it is necessary to drive the sensor element in the mixed gas atmosphere though the time period thereof is merely about ten minutes.
Although it is possible to perform the pre-treatment by an apparatus configured to inspect the element characteristics, this is not always preferable from the viewpoint of the productivity of the sensor element, because, in such a case, the inspection of the element characteristics cannot be performed during the time period of the pre-treatment.
On the other hand, using a special apparatus for performing the pre-treatment causes a problem that the size of an apparatus is increased because the gas is used, resulting in an increased cost.
Method used
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[0028]
[0029]FIG. 1 is a schematic cross-sectional view showing an outline of an exemplary configuration of a gas sensor 100. A sensor element 101 has a structure in which six layers, namely, a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6, are laminated in the mentioned order from the bottom side seen in FIG. 1, each of the layers being fainted by an oxygen-ion conductive solid electrolyte such as a zirconia (ZrO2). The solid electrolyte forming these six layers is densely airtight. The sensor element 101 is manufactured by, for example, performing a predetermined process and printing a circuit pattern on ceramic green sheets, each of which corresponds to each of the layers, then laminating the green sheets, and furthermore baking the laminated body to integrate it.
[0030]Between a lower surface of the second solid electrolyte layer 6 and an upper surface of t...
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Abstract
To provide a method for manufacturing a sensor element, by which stabilization of an electrode, which is performed prior to inspecting element characteristics, can be performed for a shorter time period and in a more reliable manner than in the conventional. The sensor element includes: an oxygen-ion conductive solid electrolyte layer; a first electrode that is formed on a surface of the oxygen-ion conductive solid electrolyte layer; and a second electrode that is formed in a space provided inside the oxygen-ion conductive solid electrolyte layer, and that is configured to reduce said predetermined gas component. As the pre-treatment, by an external power source. a voltage is applied between the first electrode and the second electrode, to thereby decompose and remove a gas component attached to the second electrode.
Description
BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a method for manufacturing a sensor element for use in a gas sensor, and particularly to a method for stabilizing the condition of an electrode.[0003]2. Description of the Background Art[0004]Conventionally, various gas sensors have been used for recognizing a concentration of a desired gas component in a measurement gas. For example, as a device for measuring a NOx concentration in a measurement gas such as a combustion gas, known is a NOx sensor having a sensor element which is formed using an oxygen-ion conductive solid electrolyte such as zirconia (ZrO2) (for example, see Japanese Patent Application Laid-Open No. 2006-284223 and Japanese Patent No. 3537983).[0005]In sensor elements of gas sensors including the NOx sensors disclosed in Japanese Patent Application Laid-Open No. 2006-284223 and Japanese Patent No. 3537983, a concentration of a measurement object gas component (object co...
Claims
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IPC IPC(8): G01R31/28G01R35/00
CPCG01R31/28G01R35/00Y10T29/49004G01N27/4074Y10T29/49002G01N27/4071
Inventor OHTSUBO, SHINJIISHIKAWA
Owner NGK INSULATORS LTD